It is customary to ground-check the performance of jet engines after over-haul or the replacement of parts. The engines are tested either in the aircraft or on a test stand by running them at full takeoff power. The resulting horizontal jet blast is very powerful and dangerous, and must be deflected to prevent possible injury to mechanics and buildings in the immediate vicinity. The blast deflectors and fences of the prior art (see for example U.S. Pat. Nos. 2,974,910, and 3,126,176) tend to suck up the ambient air behind the deflector or fence, causing notable turbulence and reverse flow. The temperatures, velocities and volumes of exhaust gases from the newer jet engines far exceed those for which the previously designed blast deflectors were intended. The greatest single problem with the prior art structures is turbulene behind the deflector. Turbulence is greatly magnified in the prior art blast fences by the spanwise flow of the high velocity gases, which swirl off the ends of the fence into the low pressure area behind the structure. This in turn forms vortices having extreme turbulence even when the small end plates shown in the prior art patents are used. These turbulent gases are very dangerous because of their temperature, velocity and the fumes which they carry.
In addition to the unsatisfactory aerodynamic performance of the prior art patents as noted above, the effective life of these blast fences is relatively short. This is because the extreme high temperature and high velocity of after burner blasts produced by military jets on take-off tend to overheat the deflecting surface and the high blast velocity creates a high pressure which causes the sheets to deform. These deformed sheets require maintenance and early replacement.
The improvement embodied by the present invention alleviates these problems. The low pressure area behind the deflector is virtually eliminated. By eliminating this low pressure area, vortices and turbulence and reverse flow are reduced. With the addition of the herein disclosed end closures, protection from jet blast is so complete that it is possible to stand behind or to the side of the improved deflector and touch the structure with no discomfort.